Car battery system

ABSTRACT

The car battery system of the present invention is provided with battery blocks  2  that retain a plurality of battery cells  1  in a stacked configuration and have terminal planes  2 A, which are coincident with terminal surfaces  1 A established by positive and negative battery cell  1  electrode terminals  13;  and with battery state detection circuits  30  that connect with the electrode terminals  13  of each battery cell  1  to detect the condition of each battery cell  1.  The car battery system implements a battery state detection circuit  30  on a circuit board  7, 87,  and the circuit board  7, 87  is mounted on a battery block  2  in a position opposite the terminal plane  2 A of the battery block  2.  Further, the positive and negative electrode terminals  13  of each battery cell  1  are connected with a circuit board  7, 87  for connection to a battery state detection circuit  30.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a car battery system with battery statedetection circuits connected to battery blocks having a plurality ofbattery cells connected in a stacked fashion.

2. Description of the Related Art

A car battery system has many battery cells stacked together andconnected in series to increase the output voltage. In this type ofbattery system, battery cell degradation is prevented by controllingbattery charging and discharging while detecting the state of eachbattery cell. Each battery cell connected in series is charged anddischarged by the same current. Remaining battery capacity is computedby integrating battery charging and discharging currents, and chargingand discharging is controlled to keep the remaining capacity within aset range. Remaining capacity is computed by adding integrated chargingcurrent values and subtracting integrated discharging current values. Inpractice, actual remaining capacity differences develop over time forbattery cells charged and discharged by the same currents. This isbecause differences in battery cell temperature and electricalcharacteristics cause variation in the actual charging and dischargingof each battery cell. If differences in actual remaining capacitydevelop, a battery cell with low remaining capacity can easily beover-discharged while a battery cell with high remaining capacity caneasily be over-charged, and this can be the cause of battery celldegradation. This is because a battery cell can be significantlydegraded by over-charging or over-discharging. Since a car batterysystem is provided with many battery cells, manufacturing cost isextremely high and extending system life-time is of utmost importance.

Battery cell degradation can be prevented by detecting the voltage ofeach battery cell and controlling actual remaining battery capacity tokeep it in a set range. Therefore, in a battery system having batteryblocks with many series-connected battery cells, battery state detectioncircuits are provided to detect the voltage of each battery cell. Thesebattery state detection circuits are disposed next to the battery blocksand are connected to the positive and negative electrode terminals ofeach battery cell via a wire-harness (refer to Japanese PatentApplication Disclosure 2008-140631).

As shown in the abbreviated view of FIG. 1 for example, a car batterysystem with many battery cells stacked together has a wire-harness 94connected to the electrode terminals 93 of each battery cell 91, andthis wire-harness 94 is connected to a battery state detection circuit90 disposed outside the battery block 92. The wire-harness 94 has manylong wire-leads 95 bundled together, and each wire-lead 95 is connectedto the electrode terminals 93 of each battery cell 91 and to the batterystate detection circuit 90. Not only is the wire-harness 94 long, butthe lengths of the wire-leads 95 connecting different battery cells 91are different. For example, wire-leads 95 connecting battery cells 91furthest from the from the battery state detection circuit 90 areextremely long. In a long wire-harness with different length wire-leads,impedances of the wire-leads are high and there can be significantimpedance differences for different wire-leads. Differences in wire-leadimpedances can be the cause of battery cell voltage detection error inthe battery state detection circuit. In particular, it is necessary forthe battery state detection circuit to detect voltage differencesbetween battery cells with extremely high precision. For example, abattery system with lithium-ion battery cells demands a very highindividual battery cell voltage detection accuracy of 0.05 V or better,and preferably 0.02 V or better. Since prior art battery systems employwire-harnesses with very long wire-leads bundled together, the largeimpedance of the wire-harness has become a cause of reduced individualbattery cell measurement accuracy.

Further, since the wire-harness of a prior art battery system bundlestogether wire-leads connected to each battery cell, the battery systemhas the drawbacks that an open circuit in the wire-harness can causefunctional failure and a short circuit between wires in the wire-harnesscan cause fire or smoke.

SUMMARY OF THE INVENTION

The present invention was developed with the object of resolving thedrawbacks described above. Thus, it is a primary object of the presentinvention to provide a car battery system that can reduce the lineimpedance for connections between each battery cell and a battery statedetection circuit, and can make line impedances uniform to enableextremely high precision voltage measurements for the many batterycells. Further, it is another object of the present invention to providea car battery system that can effectively prevent malfunction, smoke,and fire due to an open circuit or short circuit in the wire-harnessconnecting the many battery cells with a battery state detectioncircuit; and can improve reliability and safety by insuring stable,reliable detection of the condition of each battery cell by the batterystate detection circuits.

The car battery system of the present invention is provided with batteryblocks 2 that retain a plurality of battery cells 1 in a stackedconfiguration and have terminal planes 2A, which are coincident withterminal surfaces 1A established by positive and negative battery cell 1electrode terminals 13; and with battery state detection circuits 30that connect with the electrode terminals 13 of each battery cell 1 ofeach battery block 2 to detect the condition of each battery cell 1. Inthe car battery system, a battery state detection circuit 30 isimplemented by a circuit board 7, 87, and the circuit board 7, 87 ismounted on a battery block 2 in a position opposite the terminal plane2A of the battery block 2. Further, the positive and negative electrodeterminals 13 of each battery cell 1 in the car battery system areconnected with a circuit board 7, 87 for connection to a battery statedetection circuit 30.

The battery system described above has the characteristic that lineimpedances for connection between each battery cell and a battery statedetection circuit can be low and uniform allowing extremely highprecision measurement of the voltage of each of the many battery cells.This is because the circuit board for a battery state detection circuitin the battery system described above is disposed opposite the terminalplane of a battery block allowing positive and negative electrodeterminals of each battery cell to connect to the circuit board over aminimum distance.

Further, the battery system described above has the characteristic thatit can effectively prevent malfunction, smoke, and fire due to an opencircuit or short circuit in a wire-harness connecting the many batterycells with a battery state detection circuit, and it can improvereliability and safety by insuring stable, reliable detection of thecondition of each battery cell by a battery state detection circuit.This is because the circuit board for a battery state detection circuitis mounted opposite a battery block terminal plane, and the positive andnegative electrode terminals of each battery cell are connected to thecircuit board. In this configuration, a long wire-harness is not used,and electrode terminals can be connected to the circuit board, which ismounted in close proximity to battery cell electrode terminals. Wirerouting for connections between each battery cell and the circuit boardrequires no bundling, twisting, or crossing of wire-leads. Therefore,faults such as short circuits between wire-leads are reliably prevented.

The above and further objects of the present invention as well as thefeatures thereof will become more apparent from the following detaileddescription to be made in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an abbreviated plan view of a prior art car battery system;

FIG. 2 is an oblique view of a car battery system for one embodiment ofthe present invention;

FIG. 3 is an oblique view of the car battery system shown in FIG. 2 withthe upper case removed;

FIG. 4 is an exploded oblique view of the car battery system shown inFIG. 3;

FIG. 5 is a lateral cross-section view of the car battery system shownin FIG. 2;

FIG. 6 is a block diagram of a car battery system for one embodiment ofthe present invention;

FIG. 7 is a block diagram of a battery state detection circuit;

FIG. 8 is an exploded oblique view showing the stacking configurationfor battery cells and spacers.

FIG. 9 is an enlarged oblique view showing the connecting structure forelectrode terminals and connecting terminals.

FIG. 10 is an enlarged cross-section view showing another example of avoltage detection line;

FIG. 11 is an enlarged cross-section view showing another example of avoltage detection line;

FIG. 12 is an enlarged cross-section view showing another example of avoltage detection line;

FIG. 13 is an enlarged cross-section view showing another example of avoltage detection line; and

FIG. 14 is a lateral cross-section view of a car battery system foranother embodiment of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENT(S)

In the car battery system, temperature sensors 38, which are in thermalcontact with the battery cells 1 for battery temperature measurement,can be connected to the circuit board 7, 87. In this car battery system,temperature sensors can be disposed in ideal locations while insuringreliable connection by minimizing the distance between temperaturesensors and battery state detection circuits.

In the car battery system, a liquid filling opening 14 is provided onthe terminal surface 1A of each battery cell 1, and through-holes 7A,87A can be provided in the circuit board 7, 87 at positions opposite thebattery cell 1 liquid filling openings 14. In this battery system, manybattery cells can be connected together to form a battery block, acircuit board can be mounted on the battery block, and in thatconfiguration each battery cell can be filled with electrolyte. Thiseliminates the necessity to hold battery cells in a tray to avoidbattery cell expansion during electrolyte filling as in prior artbattery systems. It also eliminates any requirement to assemble abattery block by removing filled battery cells from the holding tray andapplying pressure to maintain the specified shape of expanded batterycells. Further, since the many battery cells can be filled after beingconnected together, there is no need to place the battery cells in atray for electrolyte filling. Consequently, this battery system has thecharacteristic that the electrolyte filling process can be efficientlyperformed.

In the car battery system, a safety valve exhaust opening 12 is providedon the terminal surface 1A of each battery cell 1, and gas outlet holes87B can be provided in the circuit board 87 at positions opposite thesafety valve exhaust openings 12 to pass discharged gas. If a safetyvalve opens during battery system operation and battery chemicals suchas gas are exhausted, that gas can be smoothly discharged.

In the car battery system, a safety valve exhaust opening 12 is providedon the terminal surface 1A of each battery cell 1, and a gas exhaustduct 6 can be disposed between the battery block 2 terminal plane 2A andthe circuit board 7 in a manner connecting battery cell exhaust openings12. This battery system can smoothly discharge gas exhausted from asafety valve through the gas exhaust duct, and even if the exhausted gasis high temperature gas, there are no detrimental effects on thebatteries or circuit board due to the high temperature gas.

Further, in the car battery system, a circuit board 7 can be attached tothe gas exhaust duct 6. In this battery system, a circuit board can bereliably mounted on a battery block via the gas exhaust duct, which isattached to the battery block.

Further, in the car battery system, the circuit board 7, 87 can beconnected to the positive and negative electrode terminals 13 of eachbattery cell 1 via voltage detection lines 8, 48, 58, 68, 78, and eachvoltage detection line 8, 48, 58, 68, 78 can be connected to the samelocation on each electrode terminal. In this battery system, since thevoltage detection lines connect to the same electrode terminal locationson each battery cell, the voltage drop due to electrode terminalconnection-region resistance adds equally to the voltage for eachbattery cell, and measurement error due to connection-region voltagedrop can be prevented.

The following describes embodiments based on the figures. The batterysystem is most appropriately used as a power source for an electricdriven vehicle such as a hybrid car, which is driven by both an electricmotor and an engine, or an electric automobile, which is driven by anelectric motor only.

The battery system shown in FIGS. 2-7 is provided with battery blocks 2that retain a plurality of battery cells 1 in a stacked configuration,and battery state detection circuits 30 that connect to the electrodeterminals 13 of each battery cell 1 of each battery block 2 to detectthe condition of each battery cell 1.

In a battery block 2, battery cells 1 are stacked to position theirterminal surfaces 1A, which are provided with positive and negativeelectrode terminals 13, in a single plane that is the terminal plane 2Aon the upper surface of the battery block 2. A battery holder 3 isattached outside the battery block 2 to hold the stacked battery cells1. As shown in FIG. 8, each battery cell 1 is a rectangular battery 10with a rectangular outline having a terminal surface 1A as its uppersurface in the figure, and this terminal surface 1A is provided withpositive and negative electrode terminals 13, a safety valve exhaustopening 12, and a liquid filling opening 14.

As shown in FIG. 8, a rectangular battery 10 is wide compared to itsthickness. These rectangular batteries 10, which are thinner than theyare wide, are stacked in the direction of their thickness to form abattery block 2. The rectangular batteries 10 are lithium-ionrechargeable batteries. However, the rectangular batteries can also berechargeable batteries such as nickel-hydride batteries ornickel-cadmium batteries. The rectangular batteries 10 of the figure arerectangular-shaped with wide surfaces on both sides, and those sidesurfaces are stacked against one another to form a battery block 2. Theterminal surface 1A of each rectangular battery 10 is provided withpositive and negative electrode terminals 13 protruding from both ends,and a safety valve exhaust opening 12 in the center region.

When the internal pressure of the battery cell 10 becomes greater than aset pressure, the safety valve opens to prevent excessive internalpressure rise. The safety valve houses a valve mechanism (notillustrated) that closes off the exhaust opening 12. The valve mechanismhas a membrane that breaks at a set pressure, or it is a valve with aflexible component that presses against a valve seat and opens at a setpressure. When the safety valve is opened, the interior of therectangular battery 10 is opened to the outside through the exhaustopening 12, and internal gas is exhausted to prevent internal pressurebuild-up.

Further, the positive and negative electrode terminals 13 of eachrectangular battery 10 are bent in opposite directions, and the positiveand negative electrode terminals 13 of adjacent rectangular batteries 13are also bent in opposite directions. In the battery system of thefigures, positive and negative electrode terminals 13 of adjacentrectangular batteries 10 are connected in an overlapping configurationto connect the batteries in series. As shown in FIG. 9, overlappingelectrode terminals 13 are connected by fasteners 20 such as a bolt 20Aand nut 20B. However, positive and negative electrode terminals can alsobe connected via bus-bars to connect the batteries in series. A batterysystem with adjacent rectangular batteries 10 connected in series canproduce a high output voltage. However, the battery system can alsoconnect adjacent rectangular batteries in parallel.

A battery block 2 has spacers 15 sandwiched between stacked rectangularbatteries 10. The spacers 15 insulate adjacent rectangular batteries 10.As shown in FIG. 8, a spacer 15 has a shape that fits rectangularbatteries 10 in fixed positions on both sides, and allows adjacentrectangular batteries 10 to be stacked without shifting position.Rectangular batteries 10 stacked in an insulating manner with spacers 15can have external cases 11 made of metal such as aluminum. A batteryblock can also stack and retain a plurality of battery cells withoutintervening spacers. Although not illustrated, this type of batteryblock insulates the metal surfaces of rectangular battery external casesby covering them with an insulating film. For example, plasticheat-shrink tubing or insulating coating can be used as an insulatingfilm. In addition, the external case of a rectangular battery cell canbe made of an insulating material such as plastic. These types ofrectangular batteries can be stacked together without interveningspacers to form battery blocks.

Spacers 15 stacked with the battery cells 1 are provided with coolinggaps 16 between the spacers 15 and the battery cells 1 to pass a coolinggas such as air to effectively cool the battery cells 1. The spacer 15of FIG. 8 is provided with grooves 15A in its surfaces opposite thebattery cells 1 that extend to the edges on both sides and establishcooling gaps 16 between the spacer 15 and the battery cells 1. Thespacer 15 of the figure is provided with a plurality of grooves 15Ahaving parallel orientation and disposed at given intervals. The spacer15 of the figure is provided with grooves 15A on both sides to establishcooling gaps 16 between the spacer 15 and adjacent battery cells 1. Thisstructure has the characteristic that battery cells 1 on both sides ofthe spacer 15 can be effectively cooled by cooling gaps 16 formed onboth sides of the spacer 15. However, grooves can also be provided ononly one side of the spacer to establish cooling gaps between batterycells and spacers. The cooling gaps 16 of FIGS. 3 and 4 are establishedextending in a horizontal direction and opening on the left and rightsides of the battery block 2. Ventilating air passed through the coolinggaps 16 efficiently cools battery cell 1 external cases 11 directly.This configuration has the characteristic that battery cell 1 thermalrunaway can be effectively prevented, and battery cells 1 can beefficiently cooled.

The battery holder 3, which retains battery cells 1 in a stackedconfiguration, is provided with a pair of endplates 4 that sandwichesthe battery block 2 from both ends, and connecting rails 5 connected atboth ends or mid-regions to a pair of endplates 4. Connecting rails 5are disposed at rectangular battery 10 perimeters, and both ends ormid-regions are connected to endplates 4. The battery holder 3 holds abattery block 2 of stacked battery cells 1 with endplates 4 at both endsand with connecting rails 5 disposed at rectangular battery 10 perimetersurfaces and connected to the endplates 4 at both ends. With thisstructure, the battery holder 3 securely holds a plurality of stackedrectangular batteries 10.

The endplates 4 have a rectangular shape with the same dimensions andshape as the outline of the rectangular batteries 10, and the endplates4 hold the stacked battery block 2 from both ends. An endplate 4 is madeof plastic or metal and is provided with reinforcing ribs 4A extendingvertically and horizontally on the outer surface, which is formed as asingle piece with the endplate 4. Further, the endplates 4 shown in thefigures have reinforcing metal pieces 17 fixed along their upper edges,and connecting rails 5 are connected to those reinforcing metal pieces17. This configuration has the characteristic that endplates 4reinforced with reinforcing metal pieces 17 can make robust structures,and connecting rails 5 can be solidly connected to the endplates 4. Inparticular, this configuration has the characteristic that it can makethe endplates 4 themselves strong when the endplates 4 are molded fromplastic. However, endplates do not always need to be reinforced withreinforcing metal pieces. For example, endplates can also be made ofmetal with no reinforcing metal pieces, and connecting rails can bedirectly connected to those endplates. The connecting rails 5 are madeof metal such as steel and attach at both ends or mid-regions toendplates 5 via set screws 18.

FIGS. 6 and 7 show block diagrams of the battery system. In the batterysystem of these block diagrams, a battery state detection circuit 30 isconnected to each battery cell 1. The battery state detection circuit 30shown in FIG. 7 is provided with a voltage detection circuit 31 todetect the voltage of each battery cell 1; a cell balance circuit 32 toequalize the voltage of each battery cell 1; a temperature detectioncircuit 33 to detect battery temperature; and a control circuit 34 tocontrol these detection and balance circuits, process signals input fromthose circuits, and output that data from the battery state detectioncircuit 30 via an isolated communication circuit 35. The battery systemof FIG. 6 is provided with a plurality of battery blocks 2, and signalsoutput from battery state detection circuits 30 connected to eachbattery block 2 are input to a main control circuit 36. The main controlcircuit 36 controls the battery system based on the signals input fromeach battery state detection circuit 30.

Battery state detection circuits 30 are implemented by surface-mountingon circuit boards 7. As shown in FIGS. 3-5, a circuit board 7implementing a battery state detection circuit 30 is attached oppositethe battery block 2 terminal plane 2A on the top of the battery block 2in the figures. The circuit board 7 of FIGS. 3 and 4 has both endsattached to endplates 4 via set screws 29. In addition, the circuitboard 7 of the figures is also attached via set screws 29 to the top ofthe gas exhaust duct 6, which is mounted on the battery block 2 terminalplane 2A. A circuit board 7 can be solidly mounted on the battery block2 by attaching it to the gas exhaust duct 6.

The circuit board 7 is provided with through-holes 7A to fill batterycell 1 external cases 11 with electrolyte through the liquid fillingopenings 14 established in battery cell 1 terminal surfaces 1A. Thesethrough-holes 7A are opened in positions opposite the liquid fillingopenings 14 in the battery cells 1. In this battery block 2, batterycells 1, which have not been filled with electrolyte, are stackedtogether, held between endplates 4, and the circuit board 7 is attached.In this state, each battery cell 1 is filled with electrolyte, and theliquid filling openings 14 are closed off to complete assembly of thebattery block 2. For a battery block 2 assembled in this manner, thereis no need to arrange a plurality of battery cells 1 in a holding trayto avoid cell expansion, and battery cells 1 can be filled efficientlywhile stacked together and retained in a manner avoiding cell expansion.Further, since battery cell 1 external cases 11 are filled withelectrolyte with the battery block 2 in the assembled state,malfunctions such as short circuits occurring at this process step canbe prevented allowing safe assembly.

The circuit board 7 is mounted in close proximity and in a parallelorientation with respect to the battery block 2 terminal surface 2A. Thecircuit board 7 of FIG. 5 has temperature sensors 38 mounted on itsbottom surface. The temperature sensors 38 are in thermal contact withbattery cells 1 and measure battery temperature. In this structure, thecircuit board 7 is mounted opposite the battery block 2 terminal surface2A and the temperature sensors 38 can be held in thermal contact withbattery cells 1. Electrically insulating, thermally conducting material39 is disposed between a temperature sensor 38 and a battery cell 1 toallow more accurate battery cell 1 temperature measurement. A batterystate detection circuit 30 that measures battery cell 1 temperature viatemperature sensors 38 outputs detected temperature outside the batterystate detection circuit 30. If battery temperature rises above a settemperature or drops below a set temperature, charging and dischargingcurrents are limited or cut-off.

The circuit board 7 is connected to the positive and negative electrodeterminals 13 of each battery cell 1 through voltage detection lines 8.Voltage detection lines 8 connect the positive and negative electrodeterminals 13 of each battery cell 1 with the voltage detection circuit31 in the battery state detection circuit 30 mounted on the circuitboard 7. As a result, for example, a battery block with eighty batterycells stacked together is connected to a circuit board with eighty onevoltage detection lines. The voltage detection circuit 31 measures thevoltage of each battery cell 1 via the voltage detection lines 8. Thebattery state detection circuit 30 determines the condition of thebattery cells 1 using battery cell 1 voltage measured by the voltagedetection circuit 31, and outputs results outside the battery statedetection circuit 30.

Adjacent battery cells 1 of a battery block 2 are connected in series byjoining overlapping electrode terminals 13 with fasteners 20, or byjoining electrode terminals via bus-bars. High currents flow in abattery block 2 and voltage drops are generated by the resistance ofelectrode terminal 13 connecting regions. These voltage drops increasein proportion to battery block 2 current. To prevent measurement errordue to connecting region voltage drops, voltage detection lines 8 areconnected at the same location for each battery cell 1. Specifically,voltage detection lines 8 are connected to add the connecting regionvoltage drop to the voltage for each battery cell 1.

Voltage detection lines 8 are attached at one end to an electrodeterminal 13, and at the other end to the circuit board 7. A voltagedetection line 8 is attached to an electrode terminal 13 via aconnecting terminal 41. As shown in FIG. 9, the connecting terminal 41is attached to an electrode terminal 13 via fasteners 20 that connectadjacent electrode terminals 13. The connecting terminal 41 shown inthis figure is formed from sheet metal and is provided with a connectinghole 41A at one end to insert a fastener 20 bolt 20A, and a verticalconnecting section 41 B at the other end with a long narrow rod-shapethat is bent upward to a vertical disposition. The upright connectingsection 41 B of this connecting terminal 41 is used as the voltagedetection line 8 and is inserted through the circuit board 7. Voltagedetection lines 8 inserted through the circuit board 7 are fixed to thecircuit board 7 by soldering. However, voltage detection lines can alsobe routed from both sides of the circuit board to connect the circuitboard and electrode terminals. Although not illustrated, in a batteryblock with electrode terminals connected via bus-bars, the bus-bar metalplates can be formed to establish voltage detection lines. Further,circuit board voltage detection lines can be directly connected toelectrode terminals via spot welding or laser welding without usingconnecting terminals. Voltage detection lines can also be connected toelectrode terminals via connectors.

In the battery system of FIG. 10, a voltage detection line 48 connectedto an electrode terminal 13 has a connector 42 attached at one end, andthat connector 42 mates with another connector 43 mounted on the circuitboard 7. Since a gas exhaust duct 6 is disposed at the center regions ofbattery cell 1 terminal surfaces 1A in the battery system of thefigures, connectors 42 are disposed at both sides of the terminalsurfaces 1A. The connectors 42 are disposed in fixed positions via thevoltage detection lines 48, or they can be disposed in fixed positionsby attachment to electrode terminals 13 or the gas exhaust duct 6. Withthis structure, the circuit board 7 can be pressed onto the batteryblock 2 terminal plane 2A to join the connectors 42, 43 and connect thecircuit board 7 to each electrode terminal 13.

Further, the circuit board 7 can also be connected to each electrodeterminal 13 by voltage detection lines 58, 68, 78 configured as shown inFIGS. 11-13. The voltage detection lines 58, 68 of FIGS. 11 and 12 areconductive metal wire that can deform in a flexible manner. The voltagedetection line 58 of FIG. 11 is provided with a folded region 58A at itscenter that can extend and contract. Similarly, the voltage detectionline 68 of FIG. 12 is provided with a curved region 68A at its centerthat can extend and contract. These types of structures can connect theelectrode terminals 13 of each battery cell 1 to the circuit board 7while absorbing any shift in the relative position of the circuit board7 and the battery block 2. Further, the voltage detection line 78 ofFIG. 13 connects electrode terminals 13 from both sides of the circuitboard 7. The voltage detection line 78 shown in this figure can, forexample, be a lead-wire or a lead-plate. The voltage detection line 78,which is a lead-wire or a lead-plate, has one end attached to aconnecting terminal 71, which is connected to an electrode terminal 13,and the other end connected to the upper surface of the circuit board 7by solder attachment. This voltage detection line 78 does not passthrough the circuit board 7, but rather is routed around the side edgesto connect to the top of the circuit board 7.

The voltage detection lines 8, 48, 58, 68, 78 are short resulting in lowimpedance, and each voltage detection line 8, 48, 58, 68, 78 has auniform length resulting in equal impedances. Consequently, eachelectrode terminal 13 is connected with the circuit board 7 by voltagedetection lines 8, 48, 58, 68, 78 of the same length. However, since thecircuit board 7 is disposed on the battery block 2 terminal plane 2A andvoltage detection lines 8, 48, 58, 68, 78 can be made extremely short,impedance is low and the battery system can accurately measure thevoltage of each battery cell 1 even if there is some difference in thelength of the voltage detection lines. Consequently, as shown in FIG.10, by attaching connectors 42 to mate with the connecting side of thecircuit board 7, battery cell 1 voltage can be accurately measured evenif there is some difference in the length of the voltage detection lines48 connected to each electrode terminal 13.

The battery system of FIGS. 2-5 has a gas exhaust duct 6 mounted at thecenter of the battery block 2 terminal plane 2A. This gas exhaust duct 6is provided with connecting flanges 6B projecting from both sides andpositioned above the endplates 4 to attach the gas exhaust duct 6 to theendplates 4 via set screws 19.

Further, the gas exhaust duct 6 has end regions formed in (rectangular)cylindrical shapes, and the gas exhaust duct 6 is attached to theendplates 4 with these cylindrical regions projecting out from theendplates 4 as cylindrical projections 6A. Although not illustrated,passage-ways such as exhaust ducting can connect to these cylindricalprojections 6A allowing any gas exhausted from the safety valve exhaustopening 12 of a rectangular battery 10 to be quickly discharged to theoutside.

The battery system of FIGS. 2 and 5 has the upper case 9A of its outercase 9 attached above the gas exhaust duct 6. The outer case 9 of thefigures is made up of an upper case 9A and a lower case 9B. The uppercase 9A and the lower case 9B have flanges 21 that project outward, andthese flanges 21 are connected via bolts 22 and nuts 23. In the outercase 9 of the figures, the flanges 21 are disposed at the side-walls ofthe battery block 2. In this outer case 9, the lower case 9B is attachedto the endplates 4 via set screws 24 to hold the battery block 2. Setscrews 24 pass through the lower case 9B and screw into holes (notillustrated) in the endplates 4 to attach the battery block 2 to theouter case 9. The heads of these set screws 24 protrude out from thebottom of the lower case 9B.

The upper case 9A is sheet metal formed with a top panel 9 a that coversthe top of the gas exhaust duct 6 and is connected on both sides withside panels 9 b. The bottom edges of the side panels 9 b of this uppercase 9A have flanges 21, and these flanges 21 are connected to flanges21 on the lower case 9B. Further, in the upper case 9A of the figures,step regions 9 c are provided along the boundary between the top panel 9a and the side panels 9 b, and these step regions 9 c press down on bothsides to attach to the battery block 2. The upper case 9A has the stepregions 9 c attached to the endplates 4 via set screws 24 to hold thebattery block 2. Space 25 is provided between this upper case 9A and thetop of the battery block 2, and the circuit board 7 is disposed in thisspace 25.

In addition, the outer case 9 is provided with an inlet duct 27 and anexhaust duct 26 between the side panels 9 b and the battery block 2. Inthis battery system, forced ventilation air in the inlet duct 27 ispassed through cooling gaps 16 between the rectangular batteries 10 tocool the batteries. Cooling air is discharged to the outside from theexhaust duct 26. Further, the lower case 9B is provided with projections28 that protrude downward from both sides of the battery block 2. Theseprojections 28 widen the inlet duct 27 and exhaust duct 26 to reducepressure losses in those ducts. These projections 28 also reinforce thelower case 9B and increase the bending strength of the lower case 9B. Inparticular, since the lower case 9B shown in FIG. 5 is provided withprojections 28 on both sides, bending strength is improved by the tworows of side projections 28. Further, the projections 28 provided onboth sides of the lower case 9B extend below the heads of the set screws24 that attach the battery block 2, or they extend to the same height asthe heads of the set screws 24. For a battery system with this type oflower case 9B installed on-board a car, the projections 28 set on anattachment plate allowing battery system weight to be distributed andsupported over a wide area.

In the battery system described above, a gas exhaust duct 6 is providedto discharge any gas from a battery cell 1 with an open safety valve.Therefore, any high temperature gases can be safely exhausted to theoutside. However, as shown in FIG. 14, instead of providing a gasexhaust duct, the battery system can be provided with gas outlet holes87B that pass through the circuit board 87 at locations opposite safetyvalve exhaust openings 12 allowing gases to be discharged above thecircuit board 87. Since a gas exhaust duct is not provided in thisbattery system, the circuit board 87 can be disposed in closer proximityto the battery block 2 terminal plane 2A. In the circuit board 87 of thefigure, through-holes 87A for electrolyte filling are opened oppositebattery cell 1 liquid filling openings 14, and gas outlet holes 87B fordischarging gases are opened opposite safety valve exhaust openings 12.However, the circuit board can also use the through-holes 87A as gasoutlet holes with the dual purposes of electrolyte filling and gasdischarge.

It should be apparent to those with an ordinary skill in the art thatwhile various preferred embodiments of the invention have been shown anddescribed, it is contemplated that the invention is not limited to theparticular embodiments disclosed, which are deemed to be merelyillustrative of the inventive concepts and should not be interpreted aslimiting the scope of the invention, and which are suitable for allmodifications and changes falling within the spirit and scope of theinvention as defined in the appended claims. The present application isbased on Application No. 2008-222,488 filed in Japan on Aug. 29, 2008,the content of which is incorporated herein by reference.

1. A car battery system comprising: a battery block that retains aplurality of battery cells in a stacked configuration and has a terminalplane that is coplanar with battery cell terminal surfaces establishedby positive and negative electrode terminals; and a battery statedetection circuit that is connected to the electrode terminals of eachbattery cell that makes up the battery block to detect the condition ofeach battery cell; wherein the battery state detection circuit isimplemented on a circuit board and that circuit board is attachedopposite the battery block terminal surface; and the positive andnegative electrode terminals of each battery cell are connected to thecircuit board and to the battery state detection circuit.
 2. The carbattery system as cited in claim 1 further comprising a battery holderto retain the battery block; wherein the battery holder is provided witha pair of endplates that sandwiches the battery block from both ends,and connecting rails connected to the pair of endplates; and both endsof the battery block are held between the pair of endplates, and theconnecting rails are attached to the endplates.
 3. The car batterysystem as cited in claim 2 wherein the circuit board is attached to theendplates via set screws.
 4. The car battery system as cited in claim 1wherein the battery state detection circuit is provided with a voltagedetection circuit to detect the voltage of each battery cell.
 5. The carbattery system as cited in claim 1 wherein the battery state detectioncircuit is provided with either a cell balance circuit to balancebattery cell voltages by making the voltage of each battery cell equal,or a temperature detection circuit to detect battery temperature.
 6. Thecar battery system as cited in claim 1 wherein temperature sensors,which are in thermal contact with battery cells and measure batterytemperature, are mounted on the circuit board.
 7. The car battery systemas cited in claim 1 wherein battery cells are provided with liquidfilling openings in their terminal surfaces, and the circuit board hasthrough-holes opened in positions opposite the liquid filling openingsin the battery cells.
 8. The car battery system as cited in claim 1wherein battery cells are provided with safety valve exhaust openings intheir terminal surfaces, and the circuit board has gas outlet holesopened in positions opposite the safety valve exhaust openings to passdischarged gas.
 9. The car battery system as cited in claim 1 whereinbattery cells are provided with safety valve exhaust openings in theirterminal surfaces, and a gas exhaust duct is disposed between theterminal plane of the battery block and the circuit board in a mannerconnecting the exhaust openings.
 10. The car battery system as cited inclaim 9 wherein the circuit board is attached to the gas exhaust duct.11. The car battery system as cited in claim 1 wherein the circuit boardis connected to the positive and negative electrode terminals of eachbattery cell via voltage detection lines.
 12. The car battery system ascited in claim 1 wherein the voltage detection lines are connected tothe same locations on the electrode terminals of each battery cell. 13.The car battery system as cited in claim 11 wherein the voltagedetection lines are connected to electrode terminals via connectingterminals.
 14. The car battery system as cited in claim 13 wherein theconnecting terminal is attached to an electrode terminal via fasteners,the connecting terminal has a connecting hole at one end for fastenerinsertion, the other end is shaped as a long narrow rod with a verticaldisposition as an upright connecting section, and the upright connectingsection is inserted through the circuit board as a voltage detectionline.
 15. The car battery system as cited in claim 11 wherein thevoltage detection lines connect to the circuit board via connectors. 16.The car battery system as cited in claim 11 wherein the voltagedetection lines are flexibly deformable conducting metal wire, and thecenter section of the metal wire is provided with either a folded regionor a curved region that can extend and contract.
 17. The car batterysystem as cited in claim 11 wherein the voltage detection lines areeither lead-wires or lead-plates connected from both sides of thecircuit board to the electrode terminals, and one end of a voltagedetection line is connected to a connecting terminal and the other endis connected to the upper surface of the circuit board.